"If we were to believe Republicans we would have to criminally charge Secretary [Condoleezza] Rice, Secretary [Colin] Powell, the senior staff and everyone else who received these emails. We might have to indict the entire senior level of America's national security team," the Nevada Democrat said.

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The comments came after NBC News obtained a copy of a letter from State Department Inspector General Steve Linick disclosing that two classified emails were sent to Powell's personal email when he was leading the State Department and 10 classified emails were sent to aides of Rice.

While Powell has suggested there is a difference between himself and Clinton, who used a personal email server while secretary of State, Reid stressed that the revelation undercuts a Republican investigation.

"We can now hold Republicans' allegations up to the light, see them for the flimsy, transparent attempts to score political points that they have always been," he said, dismissing the probe as an "ridiculously partisan political waste of time."

The issue has repeatedly dogged Clinton's campaign for the White House, with Democrats, including Reid, suggesting that the probe is politically motivated and aimed at undermining her bid.

Sen. Chuck Grassley (R-Iowa), who is at the center of the Senate investigation, has sent a flurry of letters seeking more information on Clinton and Huma Abedin, a top aide, and blocked State Department nominations in an effort to get a response from the department.